The exopolygalacturonate lyase PelW and the oligogalacturonate lyase Ogl, two cytoplasmic enzymes of pectin catabolism in Erwinia chrysanthemi 3937

Erwinia chrysanthemi 3937 secretes into the external medium several pectino lytic enzymes, among which are eight isoenzymes of the endo-cleaving pectat e lyases: PelA, PelB, PelC, PelD, and PelE (family 1); PelI (family 4); Pel t (family 3); and PelZ (family 5). In addition, one exe-cleaving pectate ly ase, PelX (family 3), has been found in the periplasm off. chrysanthemi. Th e E. chrysanthemi 3937 gene kdgC has been shown to exhibit a high degree of similarity to the genes pelY of Yersinia pseudotuberculosis and pelB of Er winia carotovora, which encode family 2 pectate lyases. However, no pectino lytic activity has been assigned to the KdgC protein. After verification of the corresponding nucleotide sequence, we cloned a longer DNA fragment and showed that this gene encodes a 553-amino-acid protein exhibiting an exe-c leaving pectate lyase activity. Thus, the kdgC gene was renamed pelW. PelW catalyzes the formation of unsaturated digalacturonates from polygalacturon ate or short oligogalacturonates. PelW is located in the bacterial cytoplas m. In this compartment, PelW action could complete the degradation of pecti c oligomers that was initiated by the extracellular or periplasmic pectinas es and precede the action of the cytoplasmic oligogalacturonate lyase, Ogl. Both cytoplasmic pectinases, PelW and Ogl, seem to act in sequence during oligogalacturonate depolymerization, since oligomers longer than dimers are very poor substrates for Ogl but are good substrates for PelW. The estimat ed number of binding subsites for PelW is three, extending from subsite -2 to +1, while it is probably two for Ogl, extending from subsite -1 to +1. T he activities of the two cytoplasmic lyases, PelW and Ogl, are dependent on the presence of divalent cations, since both enzymes are inhibited by EDTA . In contrast to the extracellular pectate lyases, Ca2+ is unable to restor e the activity of PelW or Ogl, while several other cations, including Co2+, Mn2+, and Ni2+, can activate both cytoplasmic lyases.